Mechanisms that Underlie the Spatial Frequency Tuning of Ganglion Cells

Abstract

Abstract: : Purpose: We have shown that a class of GABAergic amacrine cells that express neuropeptide Y (NPY/GABA cells) plays a role in shaping the spatial frequency tuning of mouse retina ganglion cells (see abstract, Nirenberg et al.) Here we examine the mechanism that underlies this tuning. Methods: The spatial frequency spectra of ganglion cells from retinas with and without NPY/GABA cells were fit to a difference-of-Gaussians model to determine the size, strength, and orientation of receptive field center and surround components. Results: NPY/GABA amacrine cells were found to play a role in shaping the size of ganglion cell receptive field surrounds. Loss of the amacrine cells caused a marked reduction in the average surround size (p<0.03, t-test), with center size controlled. The most striking result was a loss of large-diameter receptive field surrounds (order of 10x center size) in the amacrine depleted retinas (p<0.01, Χ₂). Other receptive field parameters, such as degree of asymmetry, were not affected by ablation. We developed a possible computational model of the NPY/GABA cells' role in retinal circuitry to account for their apparent role in determining receptive field surround size. Conclusion: At a given retinal eccentricity (here, central retina) ganglion cells with a wide range of different spatial frequency tunings are found. We find that this variation is due in part to diverse ganglion cell surround sizes. Here we have identified a possible role for a specific amacrine cell class, the NPY/GABA cells, in determining surround size.

Keywords: 312 amacrine cells • 559 retinal connections, networks, circuitry • 540 receptive fields